Animation Nodes - instance objects over time
The wave/scale effect is controlled by the scale of an empty (simply animate it the way you want).

The node setting is in two parts:


Main part: 


Get empty scale and generate a set of scales from it. 
Duplicates the model (a curve).
Put the result in the resulting curve.



The scale is limited between 1 and 5 in this setup but you can change it as you want.

The next nodes are making an array of scale.
Say current scale is 3.19, we want the array to be [1.19, 2.19, 3.19].
This is done using the float range node.


Sub loop:


The loop is done over the precalculated scales (above).
For each scale duplicates the input vertices and scale them.
The result is merged (reassign to the output).



The result is cumulated in a "reassign" node which is also set as output.
The model input is set as copy as we want a new circle at each iteration.